z/OS is a
64-bit operating system for
IBM mainframes, produced by
IBM. It derives from and is the successor to
OS/390, which in turn followed a string of
MVS versions. Like OS/390, z/OS combines a number of formerly separate, related products, some of which are still optional. z/OS offers the attributes of modern operating systems but also retains much of the functionality originating in the 1960s and each subsequent decade that is still found in daily use (
backward compatibility is one of z/OS's central design philosophies). z/OS was first introduced in October 2000.